Abstract: Structural defects and degree of order of natural and synthetic moissanite have been investigated by
XRD Topography and TEM. XRDT analyses of synthetic 6H-SiC wafers allowed to study extended
defects and to identify and localize coalescence of polytypes. The observed linear defects are microchannels
and dislocations. Axial screw dislocations, either parallel or slightly inclined to the c-axis,
suggest that the growth mechanism for the bulk crystals was mainly by spiral growth. Moreover, the
study of line orientations of the dislocations allow to reconstruct the growth sector evolution of the
sample. Therefore, the convex shape of the growing surface is attained by the development of
growth sectors (10l) neighbouring growth sector (001).
The coalescence of a thin lamella of a different polytype has been also localized and investigated.
The contrast analysis and the diffraction pattern of the lamella are consistent with a 15R-SiC
crystal. Such coalescence indicates local variations of growth conditions.
TEM images and selected area electron diffractions (SAEDs) strongly differentiate natural from
synthetic samples. SAED patterns with [010] incidence of natural crystals are consistent with the
6H polytype and do not show streaks along the [001] stacking direction. Synthetic samples are
comparatively much more disordered. Conventional images show high density of (001) faults, not
observed in natural samples. Consistently, SAED patterns of the [100] zone are streaked along c*.
High resolution (HR) imaging shows that synthetic samples mainly consist of (001) stacking
sequence described as (32)3. Locally mixed stacking sequence described by notation 23(3233)5,
probably referred to a long period polytype, are present.

Abstract: A review is presented of the current understanding of the dislocation configurations
observed in PVT-grown 4H- and 6H-SiC boules and CVD-grown 4H-SiC homoepitaxial layers. In
both PVT-grown boules and CVD-grown epilayers, dislocation configurations are classified
according to whether they are growth dislocations, i.e., formed during growth via the replication of
dislocations which thread the moving crystal growth front, or result from deformation processes
(under either mechanical or electrical stress) immediately following growth, during post growth
cooling, i.e., behind the crystal growth front or during device operation. Possible formation
mechanisms of growth defects in the PVT grown boules, such as axial screw dislocations and
threading edge dislocation walls are proposed. Similarly, possible origins of growth defect
configurations in CVD-grown epilayers, such as Frank faults bounded by Frank partials, BPDs and
TEDs, are also discussed. In a similar way, the origins of BPD configurations resulting from
relaxation of thermal stresses during post-growth cooling of the PVT boules are discussed. Finally,
the susceptibility of BPD configurations replicated into CVD grown epilayers from the substrate
towards Recombination Enhanced Dislocation Glide (REDG) is discussed.

Abstract: Etching of 4H-SiC wafers in molten KOH as a method for micropipe and dislocation
density analysis was investigated. The obtained results were correlated with those of the synchrotron
white beam x-ray topography. Heavily nitrogen-doped SiC shows a significantly different etching
behavior in comparison with the low-doped material. This complicates identification of different
types of threading defects. In particular, it is difficult to separate Threading Screw Dislocations
(TSD) from Threading Edge Dislocations (TED). Depending on the level of doping and thermal
history of the crystal, some of the etch pits emerging due to the 1c screw dislocations can be as large as
those due to the micropipes.